The present invention relates to a progressive ophthalmic lens suitable for undertaking a sporting activity. It also relates to a method of producing such a lens intended for an identified wearer.
The use of vision when undertaking a sporting activity may have characteristics that differ from those prevailing during everyday life. In particular, far vision and vision of the ground are very greatly used when undertaking many sports, whereas near vision is employed very little or not at all. Examples that may be mentioned are golf, jogging, tennis, cycling, etc. Possibly, near vision may be used for a limited period, such as for example for consulting a mobile telephone, for reading a map or for noting one's golf score. However, the sportsman then fixes his gaze on the mobile telephone or his map only for a short period, just sufficient to read the desired information.
Thus, very many sports require the sportsman to survey a wide visual range. For example, a golfer must be able to follow the movement of his ball, and a cyclist must not be impeded by optical distortions that might appear in the peripheral area of his visual field. To do so, it is advantageous for the sportsman to have a dynamic peripheral vision of high quality.
As is known, a progressive spectacle lens corrects the vision of a person wearing said lens for far vision differently than for near vision. Such a lens therefore provides a permanently adapted ophthalmic correction, whether the wearer looks at a far object or a near object. To do this, the lens has an optical power that varies continuously between two areas of the lens, which are dedicated to far vision and to near vision respectively. However, this variation in the optical power inherently produces an unintentional astigmatism laterally limiting the far vision and near vision areas of the lens. Because of this, it is known to adapt the design of a progressive lens according to the wearer's main activity, in order to reduce any impediment that could cause this unintentional astigmatism. For example, certain progressive lens designs have been proposed which are more adapted for working with a computer screen, while others are more adapted for driving a motor vehicle. However, undertaking a sport, such as one of those mentioned above, may require a different adaptation of the design of a progressive lens.
Thus, progressive lenses are already proposed commercially of which the design is more particularly adapted for sporting activity. These lenses have an especially enlarged far-vision area. However, this adapted is still insufficient in relation to the requirement for a wide far-vision field and good vision of the ground felt when certain sports are being undertaken.
Document U.S. Pat. No. 7,033,022 describes a particular design of progressive ophthalmic lens that possesses a very wide far-vision area. This extended area is also dedicated to intermediate vision, thereby enabling objects located at distances equal to or greater than one meter to be observed clearly by the wearer, without him moving his head. However, such a lens possesses a near-vision area in which the optical power increases continuously in the lower portion of the lens, right to the lower edge thereof. At the same time, the lens described in the above document has an area devoid of unintentional astigmatism with a width that decreases continuously between the far-vision area and the lower edge of the lens. For this reason, the design of such a progressive ophthalmic lens is referred to as a “funnel” design. The near-vision conditions that are provided by such a lens are therefore not very comfortable, especially because the wearer may have difficulties in finding that point on the lens which gives him sharp vision of a close object. Certain particular situations may even force the wearer to adopt a painful and tiring position in order to achieve satisfactory near vision.
Document EP 1 744 202, in the name of the Applicant, provides a progressive ophthalmic lens which comprises a complex surface, a prism reference point and a fitting cross, and which is suitable for being placed in front of a wearer's eye in such a way that a scan along the wearer's line of sight through the lens defines a meridian line corresponding to a trace of the line of sight intersecting with the surface. The meridian line connects an upper edge to a lower edge of the lens, passing through a far-vision reference point, the fitting cross, the prism reference point and a near-vision reference point. The fitting cross and the near-vision reference point are located at 4 mm above the prism reference point and at 14 mm below said point, respectively. The complex surface has a power addition between the far-vision and near-vision reference points and limited values for the following quantities: the cylinder normalized to the addition; the rebound in the mean sphere normalized to the addition; and the progression length. In the context of the present application, a value which is normalized to the addition means that what is considered is the quotient resulting from this value divided by the addition.
It will be recalled that the mean sphere and the cylinder of a complex surface, estimated at a point thereon, are given by the following formulae respectively:
                    Sph        =                                            n              -              1                        2                    ×                      [                                          1                                  R                  ⁢                                                                          ⁢                  1                                            +                              1                                  R                  ⁢                                                                          ⁢                  2                                                      ]                                              (                  1          ⁢          a                )                                Cyl        =                              (                          n              -              1                        )                    ×                                                                1                                  R                  ⁢                                                                          ⁢                  1                                            -                              1                                  R                  ⁢                                                                          ⁢                  2                                                                                                    (                  1          ⁢          b                )            in which n is the light refraction index or refractive index of the material of the lens at the point in question and R1 and R2 denote the radii of maximum and minimum curvature of the complex surface at the same point, these being measured in two perpendicular directions. Furthermore, the progression length is defined as the distance measured vertically on the complex surface of the lens between the fitting cross and a point on the meridian line for which the mean sphere has a difference equal to 85% of the addition in relation to the far-vision reference point.
However, the visual comfort provided by a lens as described in EP 1 744 202 may be insufficient when the person wearing this lens is undertaking a sporting activity.